The present invention relates to a printed wiring board enabling insertion components having leads to be mounted on both front and back surfaces, and its manufacturing method. More particularly, the invention relates to a printed wiring board having a non-through lead mounting hole on both surfaces, and its manufacturing method.
In the course of the development of the technology, reductions in size, weight and thickness of electronic equipment have associatively brought about progresses in high density mounting technology. For example, in mounting of components on a printed wiring board, in place of a component mounting method of obtaining electrical and mechanical coupling by inserting a lead into a through-hole, a surface mounting method of soldering a component electrode on a pad formed on a plane of the printed wiring board has mostly been used.
The surface mounting method is effective high density mounting means because of its capability of mounting surface mounted components not only on one surface but also both front and back surfaces of the printed wiring board. On the other hand, regarding a component mounted by inserting a component lead into the through-hole of the printed wiring board (referred to as inserting component having a lead, hereinafter), not only its component main body occupies a mounting surface area, but also it is impossible to mount the component on the back surface of the same position where the component lead penetrates from the front surface to the back surface. Further, a land formed in an outer edge of the through-hole limits disposition of an outer layer circuit pattern of the back surface for lead mounting.
Therefore, components still keeping insertion component shapes have mostly been limited to those, in which a great force is possibly applied to a joined portion with the printed wiring board. A component having a very large mass of a component main body, a connector or the like is an example of such components. It is because the surface mounted component pad formed on the plane of the printed wiring board is considerably lower in peel strength compared with the through-hole.
Regarding the method of mounting the inserting component having a lead on the printed wiring board, there are two methods. In one method, the component lead is inserted into the through-hole and then soldered. The other method is so-called press fitting method, in which a component with leads having elasticity in an axial radial direction is used, and electrical and mechanical connection is obtained by pressing the leads into a through-hole. As soldering is not necessary, this method has generally been used widely as a press-fitting connector on a large printed wiring board, especially in the case of a mother board or the like including a number of connectors disposed on a full surface of the printed wiring board.
Still, however, many of the connectors have large sizes while other mounted components are miniaturized. Further, the number of leads is large because of functionality, and lead pitches are narrow in most cases. Thus, constraints inevitable on pattern disposition and component mounting on the back surface of the printed wiring board are also very large.
However, the above constraints on the pattern disposition and the component mounting on the back surface can be partially reduced by using a recently disclosed technology, for example a plated non-through hole disclosed in Unexamined Japanese Patent Publication (KOKAI) No. 10-51093. A method of manufacturing a plated non-through hole by this prior art will be described by referring to schematic sectional views of FIGS. 10A to 10F.
In FIG. 10A, a reference numeral 101 denotes a double-sided or multilayer copper-clad laminate. First, a through-hole 102 is bored in the copper-clad laminate 101 by a drill. Then, first copper plating is carried out to form a through-hole plated layer 103 (FIG. 10B). Further, the through-hole 102 is filled with a resin 104 inside, and a surface of the resin is finished to be smooth after drying and curing (FIG. 10C).
Then, second copper plating is carried out to form a second plated layer 105 (FIG. 10D). Further, etching is carried out so as to achieve a predetermined surface outer layer conductor, forming a circuit pattern 106 and a land 107 (FIG. 10E). At this time, a surface component mounting pad 108 or a circuit pattern can be disposed on a behind side of a plated non-through hole.
Lastly, the resin 104 is removed by chemical solution or laser processing to form a non-through hole 109 (FIG. 10F). By using the non-through hole thus formed, as shown in FIG. 11, an insertion component 110 having a lead can be disposed on an opening side of the non-through hole, and the connection pad 108 of a surface mounted component 111 or a pattern can be disposed on an opposite side on the same position of a grid pattern.
However, in the foregoing conventional technology, it is only a surface mounted component or a pattern that can be disposed on the back surface of the insertion component having a lead, which is mounted on the printed wiring board. Thus, this technology cannot be a sufficient method for increasing a density in component mounting. In other words, if a similar insertion component having a lead can be oppositely mounted on the back surface of the insertion component having a lead, an enormous advantage can be expected.
For example, if connectors having insertion leads can be mounted on both front and back surfaces in the same position on the printed wiring board, an area necessary for the mounting can reduced to one half.
Further, in a large information processor for processing a great amount of information at a high speed, to increase a mounting density of the processor, as shown in FIG. 12, mother boards 201A and 201B have conventionally been disposed in the processor 210, and daughter boards 202 have been mounted from both front and back sides of the processor 210. However, electrical connection between the mother boards 201A and 201B has been made by a plurality of cables 203.
In recent high-speed digital transmission, however, an excessive length of a transmission path from end to end of two mother boards has caused delay of an electric signal or crosstalk between transmission lines, which has been a great obstacle to sufficient performance and reliability.
Thus, as shown in FIG. 13, if one mother board 204 is disposed on the center, and connectors are mounted to connect the daughter boards 202 to both sides thereof, a mounting density can be increased, and a transmission path can also be shortened greatly.
In this case, the front and back connectors may be shifted in position on the mother board, and connectors of through-leads may be alternately disposed. By this method, however, a number of through-holes make it difficult to draw around a pattern on all the layers and thus high-density mounting cannot be achieved.
Regarding processing of the printed wiring board, in the foregoing conventional processing method, a complex manufacturing process must be carried out, which includes drying and curing of the resin having filled the through-hole, polishing the surface to be smooth, further plating and etching, and then entirely removing of the resin supplied and cured in the previous step.
In addition, it is technically difficult to remove the resin having filled the non-through hole without any residuals. This difficulty combines with the complex manufacturing process to cause a reduction in printed wiring board yield, i.e., an increase in costs.
The present invention was made to solve the foregoing problems, and it is a first object of the invention to provide a printed wiring board having no-through lead mounting holes, which enables insertion component having leads to be mounted on both front and back surfaces of the printed wiring board, a mounting density to be increased, freedom of circuit design to be increased, and a transmission path to be shortened.
It is a second object of the invention to provide a method for manufacturing the printed wiring board having non-through lead mounting holes, which is simple, and low in defective rate, and capable of reducing costs.
The first object of the present invention is attained by a printed wiring board enabling insertion components having leads to be mounted on both upper and lower surfaces thereof, comprising:
first and second copper-clad laminates, circuit patterns being formed on the upper surface of the first laminate and lower surface of the second laminate, respectively;
an insulation layer provided between said first and second laminates; a first non-through hole formed on the upper surface of said first laminate, a bottom of the first non-through hole being closed by said insulation layer; and
a second non-through hole formed on the lower surface of said second laminate, a top end of the second non-through hole being closed by said insulation layer;
wherein inner wall surfaces of said first and second non-through holes are conductive and the insertion components can be mounted on the first and second non-through hole.
The first and second non-through holes may be disposed in a manner that the insertion components mounted on the front and back surfaces are overlapped with each other at least partially when seen from a direction vertical to the printed wiring board. With such arrangement, limitations for deciding component mounting positions on the front and back surface are reduced, thus increasing freedom of circuit design. The non-through holes opened on the front and back sides may be positioned at least partially on the same grid, i.e., the same coordinate position of the grid pattern of the printed wiring board. In this case, mounting densities on the front and back sides can be further increased. If the front and back components having leads are mounted as identical components on non-through holes on the same grid of both front and back surfaces, the components can be mounted on identical places of both front and back surfaces, further increasing mounting densities.
The second object of the present invention is attained by a method of manufacturing a printed wiring board enabling insertion components having leads to be mounted on both upper and lower sides thereof, comprising the steps of:
a) providing first and second copper-clad laminates which will make the upper and lower sides of the printed wiring board, respectively, and which are provided with plated through-holes thereon, respectively;
b) filling the through-hole of the respective laminates with a conductive paste;
c) curing the respective conductive pastes to be hardened;
d) hot-pressing the first and second laminates with each other with a prepreg as a bonding sheet being sandwiched therebetween to form a composite laminate; and
e) boring a hole in the respective conductive pastes filled in the through-holes of the respective laminates to form a non-through hole which does not penetrate to the prepreg in the composite laminate, so that the non-through holes can be used for lead mounting of the insertion components from both upper and lower side of the printed wiring board.
The prepreg is a reinforced resin made by impregnating with thermosetting or thermoplastic resin, a fiber matrix such as glass cloth, aramide paper or the like, and also serves as an electrical insulation layer in the resultant printed wiring board.
The second object of the present invention is also attained by a manufacturing method of a printed wiring board, comprising the steps of:
a) providing first and second copper-clad laminates which will make the upper and lower sides of the printed wiring board, respectively, and which is provided with a plated through-hole thereon, respectively;
b) forming a resist on the respective laminates in an area other than the plated through-hole and a land thereof;
c) plating on an area on which the resist is not formed, then removing the resist so as to form a thick copper plated layer on an inner wall surface of the respective through-holes;
d) hot-pressing said first and second laminates with each other with a prepreg as a bonding sheet being sandwiched therebetween to form a composite laminate; and
e) boring a hole on a resin component of the prepreg, which has filled in the respective non-through holes due to a pressure of the hot-press in the step c), with scraping of the respective copper plated layers, to form a non-through hole having the copper plated layer disposed on an inner surface wall thereof, so that the non-through holes can be used for lead mounting of the insertion components from both upper and lower side of the printed wiring board.
Another manufacturing method of a printed wiring board according to the present invention comprises the steps of:
a) providing first and second copper-clad laminates which will make the upper and lower sides of the printed wiring board, respectively, and which is provided with a plated through-hole thereon, respectively;
b) forming a resist on the respective laminates in an area other than the plated through-hole and a land thereof;
c) plating on an area on which the resist is not formed, then removing the resist so as to form a thick copper plated layer on an inner wall surface of the respective through-holes;
d) hot-pressing said first and second laminates with each other with a prepreg as a bonding sheet being sandwiched therebetween to form a composite laminate; and
e) boring a hole on a resin component of the prepreg, which has filled in the respective non-through holes due to a pressure of the hot-press in the step c), with scraping of the respective copper plated layers, to form a non-through hole having the copper plated layer disposed on an inner surface wall thereof, so that the non-through holes can be used for lead mounting of the insertion components from both upper and lower side of the printed wiring board
Another method of manufacturing a printed wiring board according to the present invention comprises the steps of:
a) providing first and second copper-clad laminates which will make the upper and lower sides of the printed wiring board, respectively, and which is provided with a plated through-hole thereon, respectively;
b) hot-pressing said first and second laminates with each other with a prepreg as a bonding sheet being sandwiched therebetween to form a composite laminate; a resin component of the prepreg having low flowability so that the respective through-holes is closed by the prepreg to form a non-through hole;
c) laminating resin films each having a copper foil layer thereon on upper and lower surfaces of said composite laminate while setting the respective copper foil layers outside;
d) forming an outer layer circuit pattern on the respective copper foil layers by etching processing; and.
e) removing the resin films remaining on an opening of the non-through hole by laser beam, so that the non-through holes can be used for lead mounting of the insertion components from both upper and lower side of the printed wiring board.
Yet another method of manufacturing a printed wiring board according to the present invention comprises the steps of:
a) providing first and second copper-clad laminates which will make the upper and lower sides of the printed wiring board, respectively, and which is provided with a plated through-hole thereon, respectively;
b) hot-pressing said first and second laminates with each other with a first prepreg as a bonding sheet being sandwiched therebetween to form a composite laminate; a resin component of the first prepreg having low flowability so that the respective through-holes is closed by the prepreg to form a non-through hole;
c) laminating a second prepreg, a resin component of which has low flowability, on each of upper and lower surfaces of said composite laminate, the second prepreg having an opening corresponding an opening of the non-through hole;
d) covering the opening of the respective non-through holes exposed on the upper and lower surfaces of said composite laminate with a heat resistant resin films;
e) laminating one-side copper-clad laminate, which has a base material layer and a copper layer thereon, on each of the upper and lower surfaces of the product of step d) while disposing the copper layer outside, followed by hot-pressing;
f) etching the one-side copper-clad laminates to form outer layer circuit patterns, and to remove the copper layers positioned on the openings of the non-through holes to expose the base material layers;
g) removing the base material layers covering the openings of the non-through holes by end mill processing, to expose the heat resistant resin film outside; and
h) removing the heat resistant resin films from the openings of the non-through holes, so that the non-through holes can be used for lead mounting of the insertion components from both upper and lower side of the printed wiring board.
According to the present invention, the non-through holes opened on both front (or upper) and back (or back) surfaces of the printed wiring board can be formed, and the insertion components can be mounted on optional positions of the printed wiring board from both front and back sides. Therefore, it is possible to secure a high mounting density while obtaining joining strength, which has been impossible by the planar pad for joining the surface mounted components to the printed wiring board.